OTFS - Orthogonal Time Frequency Space

TL;DR

OTFS is a novel 2D modulation technique that maps information onto the Delay-Doppler domain, transforming the wireless channel into a stable, non-fading environment to enhance MIMO and 5G performance.

Contribution

Introduces OTFS, a new modulation scheme that converts the wireless channel into a stable domain, enabling improved capacity and pilot multiplexing for Massive MIMO systems.

Findings

OTFS converts fading channels into non-fading, stable interactions.

All QAM symbols experience the same channel in OTFS.

OTFS achieves near-capacity throughput scaling with MIMO order.

Abstract

In this paper we introduce a new 2D modulation technique called OTFS (Orthogonal Time Frequency & Space) that transforms information carried in the Delay-Doppler coordinate system to the familiar time-frequency domain utilized by traditional modulation schemes such as OFDM, CDMA and TDMA. OTFS converts the fading, time-varying wireless channel into a non-fading, time-independent interaction revealing the underlying geometry of the wireless channel. In this new formulation, all QAM symbols experience the same channel and all Delay-Doppler diversity branches of the channel are coherently combined. Reference signal multiplexing is done in the time-independent Delay-Doppler domain, achieving high density pilot packing, which is a crucial requirement for Massive MIMO. Regardless of the Doppler scenario, OTFS enables approaching channel capacity through linear scaling of throughput with MIMO order, thus realizing the full promise of Massive MIMO throughput gains even in challenging 5G deployment settings.